1. Field of the Invention
The present invention relates to a lens drive unit including a lens holding frame for holding a lens and a lens moving mechanism for slidingly move the lens holding frame using a drive source, and in particular to a installing structure thereof.
2. Description of the Related Art
For optical zooming system of an imaging device, a system in which a plurality of lens groups (a zooming lens group, a focus lens group) is provided, and the system in which these lens groups are made to move in the direction of an optical axis to zoom and focus. A lens drive unit provide the lens holding frame which is holding a lens along the optical axis are arranged in series so as to be able to slide in the optical axis direction, and it make a lens holding frame to slide by a drive source. For the drive source to slidingly move the lens group holding frame, a motor is widely used. Then, it controlling precisely positions of the lens groups by a mechanism which is provided that detects a position of the lens group holding frame by using detection means and controls the motor in response to the position of the lens group holding frame.
For example, Japanese Patent Application Publication No. 2004-133054 discloses a lens barrel in which include a second group lens as a zoom lens are held by a second group frame and a third group lens as a focus lens are held by a third group frame, then a first step motor for driving the second group frame to move in front-back direction and a second step motor for driving the third group frame to move in front-back direction are fixed to a inside of a left side wall as a first outer wall of a fixed frame at the left side of each frames. The lens barrel includes detection means for detecting a position of the holding frame, and a motor terminal provided in a motor unit and the detection means are connected to a flexible printed circuit board and controlled. A lens drive unit disclosed in Japanese Patent Application Publication No. 2004-133054, for the purposes of miniaturization and a simplified structure, has a drive mechanism and the lens groups arranged adjacent to each other.
In the conventional technology described above, dust may unavoidably come into the inside of a lens barrel. Dust is likely to gather particularly to a motor because it generates heat due to its operation, and when a drive mechanism and a lens group are, as disclosed in Japanese Patent Application Publication No. 2004-133054, arranged adjacent to each other, dust is also likely to gather to the lens group in conjunction with motor operation. As a result, dust may affect imaging performance due to its attachment to a lens or cause a malfunction of a lens group holding frame due to its attachment to the drive mechanism, thus possibly causing adverse effect.
Concerning this point, in the case of a collapsible lens barrel, there is an example in which a foreign substance removal mechanism is provided at a gap or inside of the lens barrel which is likely to through enter dirt or dust. The collapsible lens barrel, for example, an image pickup device disclosed in Japanese Patent Application Publication No. 2006-251197, includes an outer tube and an inner tube which situate inside of a fixed cylinder and slide back and forth from a front end of the fixed cylinder in the direction of an optical axis, and the outer tube hold an auto focus lens group and the inner tube hold a zoom lens group. Then, for zooming and focusing, drive force of a drive motor is transmitted to a gear to slide the outer tube and the inner tube in the direction of an optical axis, thus making a small gap lead from the outside. To prevent a foreign substance from entering into the inside of the lens barrel through the gap in this sliding portion, an adhesive layer is provided in the gap portion to cause the foreign substance to adhere thereto.
However, a non-collapsible lens barrel according to Japanese Patent Application Publication No. 2004-133054, compared with a collapsible lens barrel, has an advantage that a mechanism thereof can be miniaturized. Besides, a mechanism of a lens drive unit is getting complicatedly to set detection means and control means are provided to control a position of a lens group holding frame, and accordingly, it has been a challenge on how to lay out a component for the purpose of miniaturization, and when a foreign substance removal mechanism is further added, it is difficult to lay out a small lens barrel.
Therefore, an object of the present invention is to provide a lens drive unit installation structure which enhances keeping out dust to improve reliability and realizes miniaturization and easiness to assemble.